test: reset readline configuration for justrun too

We already reset readline configuration in interactive_tarantool.lua.
In particular this fixes gh_8613_new_cli_behaviour_test run with my custom
.inputrc.

Follows up ground works done for tarantool#7774

NO_DOC=test harness
NO_TEST=test harness
NO_CHANGELOG=test harness

test/justrun.lua

@@ -72,6 +72,7 @@ function justrun.tarantool(dir, env, args, opts)
     local opts = opts or {}
     assert(type(opts) == 'table')
 
+    env['INPUTRC'] = '/dev/null'
     local tarantool_exe = arg[-1]
     -- Use popen.shell() instead of popen.new() due to lack of
     -- cwd option in popen (gh-5633).